System and method for detecting tamponade

ABSTRACT

Systems, methods, and devices for determining occurrences of a tamponade condition are disclosed. One exemplary method includes monitoring an accelerometer signal of a leadless cardiac pacemaker attached to a heart wall, determining if a tamponade condition of the patient&#39;s heart is indicated based at least in part on the monitored accelerometer signal, and in response to determining that the tamponade condition is indicated, providing a notification of the tamponade condition for use by a physician to take corrective action.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/211,333 filed on Aug. 28, 2015, the disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure generally relates to systems, devices, and methods for detecting a tamponade condition, and more particularly, to systems, devices, and methods for detecting a tamponade condition using one or more signals sensed by an implanted medical device.

BACKGROUND

Pacing instruments can be used to treat patients suffering from various heart conditions that result in a reduced ability of the heart to deliver sufficient amounts of blood to a patient's body. These heart conditions may lead to rapid, irregular, and/or inefficient heart contractions. To help alleviate some of these conditions, various devices (e.g., pacemakers, defibrillators, etc.) may be implanted in a patient's body. Such devices may monitor and provide electrical stimulation to the heart to help the heart operate in a more normal, efficient and/or safe manner. In some cases, such devices may be attached, at least partially, to the heart.

SUMMARY

The present disclosure generally relates to systems, devices, and methods for detecting a tamponade condition, and more particularly, to systems, devices, and methods for detecting a tamponade condition using one or more signals sensed by an implanted medical device. In a first illustrative embodiment, a leadless cardiac pacemaker for use in pacing a patient's heart may comprise a plurality of electrodes, an accelerometer for providing an accelerometer signal. The leadless cardiac pacemaker may further comprise a controller operatively coupled to the plurality of electrodes and the accelerometer. The leadless cardiac pacemaker may be implanted into a patient's heart and attached to a wall of the patient's heart using one or more fixation elements. In some instances, fixing the fixation elements to the patient's heart may cause a tamponade condition. In some instances, the controller may be configured to monitor the accelerometer signal of the leadless cardiac pacemaker and determine if a tamponade condition of the patient's heart is indicated based at least in part on the monitored accelerometer signal. If the controller determines that a tamponade condition is indicated, the controller may provide a notification of the tamponade condition for use by a physician to take corrective action.

Additionally, or alternatively, in some embodiments according to the first illustrative embodiment, to determine if a tamponade condition of the patient's heart is indicated based at least in part on the monitored accelerometer signal, the controller may be configured to identify a characteristic of the accelerometer signal, determine if the identified characteristic changes (e.g. diminishes) over time, and determine that the tamponade condition is indicated if the identified characteristic of the of the accelerometer signal changes (e.g. diminishes) over time.

Additionally, or alternatively, in any of the above embodiments according to the first illustrative embodiment, the identified characteristic may comprise a peak amplitude of the accelerometer signal.

Additionally, or alternatively, in any of the above embodiments according to the first illustrative embodiment, the identified characteristic may comprise a peak amplitude of an integral of the accelerometer signal.

Additionally, or alternatively, in any of the above embodiments according to the first illustrative embodiment, determining if the identified characteristic diminishes over time may comprise determining if the identified characteristic falls below a predetermined threshold.

Additionally, or alternatively, in any of the above embodiments according to the first illustrative embodiment, wherein the accelerometer signal may represent one axis of a multi-axis accelerometer.

Additionally, or alternatively, in any of the above embodiments according to the first illustrative embodiment, the accelerometer signal may represent a summed signal of all axes of a multi-axis accelerometer.

Additionally, or alternatively, in any of the above embodiments according to the first illustrative embodiment, to provide the notification, the controller may be configured to communicate a message to an external device programmer.

Additionally, or alternatively, in any of the above embodiments according to the first illustrative embodiment, the notification of the tamponade condition may be communicated using two or more of the plurality of electrodes of the leadless cardiac pacemaker.

Additionally, or alternatively, in any of the above embodiments according to the first illustrative embodiment, to determine if a tamponade condition of the patient's heart is indicated based at least in part on the monitored accelerometer signal, the controller may be configured to determine if a feature of the accelerometer signal falls below a first threshold.

Additionally, or alternatively, in any of the above embodiments according to the first illustrative embodiment, to determine if a tamponade condition of the patient's heart is indicated based at least in part on the monitored accelerometer signal, the controller may be further configured to determine if the feature of the accelerometer signal rises above a second threshold within a predetermined period of time, and determine that the tamponade condition is indicated if the feature of the accelerometer signal does not rise above the second threshold within the predetermined period of time.

Additionally, or alternatively, in any of the above embodiments according to the first illustrative embodiment, to determine if a tamponade condition of the patient's heart is indicated based at least in part on the monitored accelerometer signal, the controller may be further configured to determine whether the feature of the accelerometer signal has diminished below a second threshold value before rising above a third threshold value, and determine that the tamponade condition is indicated if the feature of the accelerometer signal has diminished below the second threshold value before rising above the third threshold value.

Additionally, or alternatively, in any of the above embodiments according to the first illustrative embodiment, the third threshold value may be less than the first threshold value.

Additionally, or alternatively, in any of the above embodiments according to the first illustrative embodiment, the leadless cardiac pacemaker may further comprise a pressure sensor, and the controller the controller may be further configured to monitor a cardiac electrical signal sensed via the plurality of electrodes, determine if a tamponade condition of the patient's heart is indicated based at least in part on the sensed cardiac electrical signal, and in response to determining that the tamponade condition is indicated, provide a notification of the tamponade condition for use by a physician to take corrective action.

Additionally, or alternatively, in any of the above embodiments according to the first illustrative embodiment, to determine if a tamponade condition of the patient's heart is indicated based at least in part on the intracardiac signal, the controller may be configured to determine if a detected peak amplitude of the intracardiac pressure signal diminishes below a threshold value.

In a second illustrative embodiment, a method for detecting a tamponade condition of a patient's heart after attachment of a leadless cardiac pacemaker to the patient's heart, the leadless cardiac pacemaker having an accelerometer that produces an accelerometer signal, may comprise monitoring the accelerometer signal of the leadless cardiac pacemaker, determining if a tamponade condition of the patient's heart is indicated based at least in part on the monitored accelerometer signal, and in response to determining that the tamponade condition is indicated, providing a notification of the tamponade condition for use by a physician to take corrective action.

Additionally, or alternatively, in any of the above embodiments according to the second illustrative embodiment, the determining step may comprise identifying a characteristic of the accelerometer signal, determining if the identified characteristic diminishes over time, and determining that the tamponade condition is indicated if the identified characteristic of the of the accelerometer signal diminishes over time.

Additionally, or alternatively, in any of the above embodiments according to the second illustrative embodiment, the identified characteristic may comprise a peak amplitude of the accelerometer signal.

Additionally, or alternatively, in any of the above embodiments according to the second illustrative embodiment, the identified characteristic may comprise a peak amplitude of an integral of the accelerometer signal.

Additionally, or alternatively, in any of the above embodiments according to the second illustrative embodiment, the accelerometer signal may represent one axis of a multi-axis accelerometer.

Additionally, or alternatively, in any of the above embodiments according to the second illustrative embodiment, the accelerometer signal may represent a summed signal of all axes of a multi-axis accelerometer.

Additionally, or alternatively, in any of the above embodiments according to the second illustrative embodiment, determining if the identified characteristic diminishes over time may comprise determining if the identified characteristic falls below a predetermined threshold.

Additionally, or alternatively, in any of the above embodiments according to the second illustrative embodiment, the leadless cardiac pacemaker may perform the monitoring, determining and providing steps.

Additionally, or alternatively, in any of the above embodiments according to the second illustrative embodiment, the leadless cardiac pacemaker may perform the monitoring step.

Additionally, or alternatively, in any of the above embodiments according to the second illustrative embodiment, an external device programmer may perform one or more of the monitoring, determining and providing steps.

Additionally, or alternatively, in any of the above embodiments according to the second illustrative embodiment, providing the notification may comprise communicating a message from the leadless cardiac pacemaker for reception by an external device programmer.

In a third illustrative embodiment, a leadless cardiac pacemaker for use in pacing a patient's heart may comprise a plurality of electrodes, an accelerometer for providing an accelerometer signal, and a controller operatively coupled to the plurality of electrodes and the accelerometer. In at least some embodiments, the controller may be configured to monitor the accelerometer signal of the accelerometer over time, determine if a tamponade condition of the patient's heart is indicated based at least in part on the monitored accelerometer signal, and, in response to determining that the tamponade condition is indicated, communicate a notification of the tamponade condition for use by a physician to take corrective action.

Additionally, or alternatively, in any of the above embodiments according to the third illustrative embodiment, the notification of the tamponade condition may be communicated using two or more of the plurality of electrodes of the leadless cardiac pacemaker.

Additionally, or alternatively, in any of the above embodiments according to the third illustrative embodiment, to determine if the tamponade condition of the patient's heart is indicated, the controller may be configured to identify a characteristic of the accelerometer signal, determine if the identified characteristic diminishes over time, and determine that the tamponade condition is indicated if the identified characteristic of the of the accelerometer signal diminishes over time.

Additionally, or alternatively, in any of the above embodiments according to the third illustrative embodiment, the identified characteristic may comprise a peak amplitude of the accelerometer signal.

Additionally, or alternatively, in any of the above embodiments according to the third illustrative embodiment, the identified characteristic may comprise a peak amplitude of an integral of the accelerometer signal.

In a fourth illustrative embodiment, a leadless cardiac pacemaker may comprise a plurality of electrodes, an accelerometer for providing an accelerometer signal, a controller operatively coupled to the plurality of electrodes and the accelerometer. In at least some embodiments, the controller may be configured to monitor an indication of a range of physical motion of a patient's heart over time using the accelerometer signal, determine if the indication of the range of physical motion of the patient's heart reduces over time by at least a predefined amount, and, if it is determined that the indication of the range of physical motion of the patient's heart has reduced over time by at least the predefined amount, communicate a notification of a possible tamponade condition for reception by a remote device that is remote from the leadless cardiac pacemaker.

Additionally, or alternatively, in any of the above embodiments according to the fourth illustrative embodiment, the controller may be further configured to monitor a heart rate of the patient's heart over time and to determine if the heart rate increases over time by at least a predetermined heart rate amount.

Additionally, or alternatively, in any of the above embodiments according to the fourth illustrative embodiment, the controller may only communicate a notification of the possible tamponade condition if it is determined that the indication of the range of physical motion of the patient's heart has reduced over time by at least the predefined amount and the heart rate of the patient's heart has increased over time by at least the predetermined heart rate amount.

Additionally, or alternatively, in any of the above embodiments according to the fourth illustrative embodiment, the notification of the possible tamponade condition may be communicated using two or more of the plurality of electrodes of the leadless cardiac pacemaker.

The above summary is not intended to describe each embodiment or every implementation of the present disclosure. Advantages and attainments, together with a more complete understanding of the disclosure, will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of the following description of various illustrative embodiments in connection with the accompanying drawings, in which:

FIG. 1 is a schematic block diagram of an illustrative leadless cardiac pacemaker (LCP) according to one embodiment of the present disclosure;

FIG. 2 is a schematic block diagram of another illustrative medical device that may be used in conjunction with the LCP of FIG. 1;

FIG. 3 is a schematic diagram of an exemplary medical system that includes multiple LCPs and/or other devices in communication with one another;

FIG. 4 is a schematic diagram of a system including an LCP and another medical device, in accordance with another embodiment of the present disclosure;

FIG. 5 is a graph showing an illustrative cardiac electrical signal and illustrative accelerometer signals detected by an LCP;

FIG. 6 is a graph showing an illustrative cardiac electrical signal and an illustrative accelerometer signal detected by an LCP;

FIG. 7 is a graph showing an illustrative accelerometer signal detected by an LCP showing multiple thresholds, in accordance with techniques of the present disclosure;

FIG. 8 is a graph showing an illustrative accelerometer signal detected by an LCP showing multiple thresholds, in accordance with techniques of the present disclosure; and

FIG. 9 is a graph showing an illustrative accelerometer signal detected by an LCP showing multiple thresholds, in accordance with techniques of the present disclosure.

While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of embodiment in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit aspects of the disclosure to the particular illustrative embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure.

DESCRIPTION

The following description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The description and the drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the disclosure.

This disclosure describes systems, devices, and methods for detecting a tamponade condition. Cardiac tamponade is a medical condition characterized by compression of the heart due to an accumulation of fluid in the pericardial sac. When a patient is experiencing cardiac tamponade, the electrical system of the heart may be functioning normally. The heart may still be generating intrinsic electrical signals in a normal rhythm, and the generated signals may propagate throughout the heart in a normal fashion. However, since the heart is being compressed by fluid in the pericardial sac, the heart muscle may not be able to relax from a contracted state, thereby limiting the ability of the heart to sufficiently pump blood.

Specifically in relation to medical devices, tamponade may be caused by attaching a medical device or leads of the medical device to the heart. Generally, a medical device or lead may have a fixation element to securely place the device or lead at a location on or within the heart. During implantation, the fixation element may end up puncturing through the heart wall or an artery or other vessel on the outside of the heart, resulting in a leak of blood between the heart muscle and the pericardial sac. As the leak continues, more blood may seep between the heart muscle and the pericardial sac, resulting in continually decreasing pumping action, potentially resulting in a dangerous situation for the patient. The present disclosure describes devices, systems, and techniques for monitoring one or more signals to determine whether a tamponade condition is occurring.

FIG. 1 is a conceptual schematic block diagram of an exemplary leadless cardiac pacemaker (LCP) that may be implanted on the heart or within a chamber of the heart and may operate to sense physiological signals and parameters and deliver one or more types of electrical stimulation therapy to the heart of the patient. Example electrical stimulation therapy may include bradycardia pacing, rate responsive pacing therapy, cardiac resynchronization therapy (CRT), anti-tachycardia pacing (ATP) therapy and/or the like. As can be seen in FIG. 1, LCP 100 may be a compact device with all components housed within LCP 100 or directly on housing 120. In some instances, LCP 100 may include communication module 102, pulse generator module 104, electrical sensing module 106, mechanical sensing module 108, processing module 110, energy storage module 112, and electrodes 114.

As depicted in FIG. 1, LCP 100 may include electrodes 114, which can be secured relative to housing 120 and electrically exposed to tissue and/or blood surrounding LCP 100. Electrodes 114 may generally conduct electrical signals to and from LCP 100 and the surrounding tissue and/or blood. Such electrical signals can include communication signals, electrical stimulation pulses, and intrinsic cardiac electrical signals, to name a few. Intrinsic cardiac electrical signals may include electrical signals generated by the heart and may be represented by an electrocardiogram (ECG).

Electrodes 114 may include one or more biocompatible conductive materials such as various metals or alloys that are known to be safe for implantation within a human body. In some instances, electrodes 114 may be generally disposed on either end of LCP 100 and may be in electrical communication with one or more of modules 102, 104, 106, 108, and 110. In embodiments where electrodes 114 are secured directly to housing 120, an insulative material may electrically isolate the electrodes 114 from adjacent electrodes, housing 120, and/or other parts of LCP 100. In some instances, some or all of electrodes 114 may be spaced from housing 120 and connected to housing 120 and/or other components of LCP 100 through connecting wires. In such instances, the electrodes 114 may be placed on a tail (not shown) that extends out away from the housing 120. As shown in FIG. 1, in some embodiments, LCP 100 may include electrodes 114′. Electrodes 114′ may be in addition to electrodes 114, or may replace one or more of electrodes 114. Electrodes 114′ may be similar to electrodes 114 except that electrodes 114′ are disposed on the sides of LCP 100. In some cases, electrodes 114′ may increase the number of electrodes by which LCP 100 may deliver communication signals and/or electrical stimulation pulses, and/or may sense intrinsic cardiac electrical signals, communication signals, and/or electrical stimulation pulses.

Electrodes 114 and/or 114′ may assume any of a variety of sizes and/or shapes, and may be spaced at any of a variety of spacings. For example, electrodes 114 may have an outer diameter of two to twenty millimeters (mm). In other embodiments, electrodes 114 and/or 114′ may have a diameter of two, three, five, seven millimeters (mm), or any other suitable diameter, dimension and/or shape. Example lengths for electrodes 114 and/or 114′ may include, for example, one, three, five, ten millimeters (mm), or any other suitable length. As used herein, the length is a dimension of electrodes 114 and/or 114′ that extends away from the outer surface of the housing 120. In some instances, at least some of electrodes 114 and/or 114′ may be spaced from one another by a distance of twenty, thirty, forty, fifty millimeters (mm), or any other suitable spacing. The electrodes 114 and/or 114′ of a single device may have different sizes with respect to each other, and the spacing and/or lengths of the electrodes on the device may or may not be uniform.

In the embodiment shown, communication module 102 may be electrically coupled to electrodes 114 and/or 114′ and may be configured to deliver communication pulses to tissues of the patient for communicating with other devices such as sensors, programmers, other medical devices, and/or the like. Communication signals, as used herein, may be any modulated signal that conveys information to another device, either by itself or in conjunction with one or more other modulated signals. In some embodiments, communication signals may be limited to sub-threshold signals that do not result in capture of the heart yet still convey information. The communication signals may be delivered to another device that is located either external or internal to the patient's body. In some instances, the communication may take the form of distinct communication pulses separated by various amounts of time. In some of these cases, the timing between successive pulses may convey information. Communication module 102 may additionally be configured to sense for communication signals delivered by other devices, which may be located external or internal to the patient's body.

Communication module 102 may communicate to help accomplish one or more desired functions. Some example functions include delivering sensed data, using communicated data for determining occurrences of events such as arrhythmias, coordinating delivery of electrical stimulation therapy, and/or other functions. In some cases, LCP 100 may use communication signals to communicate raw information, processed information, messages and/or commands, and/or other data. Raw information may include information such as sensed electrical signals (e.g. a sensed ECG), signals gathered from coupled sensors, and the like. In some embodiments, the processed information may include signals that have been filtered using one or more signal processing techniques. Processed information may also include parameters and/or events that are determined by the LCP 100 and/or another device, such as a determined heart rate, timing of determined heartbeats, timing of other determined events, determinations of threshold crossings, expirations of monitored time periods, accelerometer signals, activity level parameters, blood-oxygen parameters, blood pressure parameters, heart sound parameters, and the like. Messages and/or commands may include instructions or the like directing another device to take action, notifications of imminent actions of the sending device, requests for reading from the receiving device, requests for writing data to the receiving device, information messages, and/or other messages commands.

In at least some embodiments, communication module 102 (or LCP 100) may further include switching circuitry to selectively connect one or more of electrodes 114 and/or 114′ to communication module 102 in order to select which electrodes 114 and/or 114′ that communication module 102 delivers communication pulses. It is contemplated that communication module 102 may be communicating with other devices via conducted signals, radio frequency (RF) signals, optical signals, acoustic signals, inductive coupling, and/or any other suitable communication methodology. Where communication module 102 generates electrical communication signals, communication module 102 may include one or more capacitor elements and/or other charge storage devices to aid in generating and delivering communication signals. In the embodiment shown, communication module 102 may use energy stored in energy storage module 112 to generate the communication signals. In at least some examples, communication module 102 may include a switching circuit that is connected to energy storage module 112 and, with the switching circuitry, may connect energy storage module 112 to one or more of electrodes 114/114′ to generate the communication signals.

As shown in FIG. 1, a pulse generator module 104 may be electrically connected to one or more of electrodes 114 and/or 114′. Pulse generator module 104 may be configured to generate electrical stimulation pulses and deliver the electrical stimulation pulses to tissues of a patient via one or more of the electrodes 114 and/or 114′ in order to effectuate one or more electrical stimulation therapies. Electrical stimulation pulses as used herein are meant to encompass any electrical signals that may be delivered to tissue of a patient for purposes of treatment of any type of disease or abnormality. For example, when used to treat heart disease, the pulse generator module 104 may generate electrical stimulation pacing pulses for capturing the heart of the patient, i.e. causing the heart to contract in response to the delivered electrical stimulation pulse. In some of these cases, LCP 100 may vary the rate at which pulse generator 104 generates the electrical stimulation pulses, for example in rate adaptive pacing. In other embodiments, the electrical stimulation pulses may include defibrillation/cardioversion pulses for shocking the heart out of fibrillation or into a normal heart rhythm. In yet other embodiments, the electrical stimulation pulses may include anti-tachycardia pacing (ATP) pulses. It should be understood that these are just some examples. When used to treat other ailments, the pulse generator module 104 may generate electrical stimulation pulses suitable for neurostimulation therapy or the like. Pulse generator module 104 may include one or more capacitor elements and/or other charge storage devices to aid in generating and delivering appropriate electrical stimulation pulses. In at least some embodiments, pulse generator module 104 may use energy stored in energy storage module 112 to generate the electrical stimulation pulses. In some particular embodiments, pulse generator module 104 may include a switching circuit that is connected to energy storage module 112 and may connect energy storage module 112 to one or more of electrodes 114/114′ to generate electrical stimulation pulses.

LCP 100 may further include an electrical sensing module 106 and mechanical sensing module 108. Electrical sensing module 106 may be configured to sense intrinsic cardiac electrical signals conducted from electrodes 114 and/or 114′ to electrical sensing module 106. For example, electrical sensing module 106 may be electrically connected to one or more electrodes 114 and/or 114′ and electrical sensing module 106 may be configured to receive cardiac electrical signals conducted through electrodes 114 and/or 114′ via a sensor amplifier or the like. In some embodiments, the cardiac electrical signals may represent local information from the chamber in which LCP 100 is implanted. For instance, if LCP 100 is implanted within a ventricle of the heart, cardiac electrical signals sensed by LCP 100 through electrodes 114 and/or 114′ may represent ventricular cardiac electrical signals. Mechanical sensing module 108 may include, or be electrically connected to, various sensors, such as accelerometers, including multi-axis accelerometers such as two- or three-axis accelerometers, gyroscopes, including multi-axis gyroscopes such as two- or three-axis gyroscopes, blood pressure sensors, heart sound sensors, piezoelectric sensors, blood-oxygen sensors, and/or other sensors which measure one or more physiological parameters of the heart and/or patient. Mechanical sensing module 108, when present, may gather signals from the sensors indicative of the various physiological parameters. Both electrical sensing module 106 and mechanical sensing module 108 may be connected to processing module 110 and may provide signals representative of the sensed cardiac electrical signals and/or physiological signals to processing module 110. Although described with respect to FIG. 1 as separate sensing modules, in some embodiments, electrical sensing module 106 and mechanical sensing module 108 may be combined into a single module. In at least some examples, LCP 100 may only include one of electrical sensing module 106 and mechanical sensing module 108. In some cases, any combination of the processing module 110, electrical sensing module 106, mechanical sensing module 108, communication module 102, pulse generator module 104 and/or energy storage module may be considered a controller of the LCP 100.

Processing module 110 may be configured to direct the operation of LCP 100 and may, in some embodiments, be termed a controller. For example, processing module 110 may be configured to receive cardiac electrical signals from electrical sensing module 106 and/or physiological signals from mechanical sensing module 108. Based on the received signals, processing module 110 may determine, for example, occurrences and types of arrhythmias and other determinations such as whether LCP 100 has become dislodged. Processing module 110 may further receive information from communication module 102. In some embodiments, processing module 110 may additionally use such received information to determine occurrences and types of arrhythmias and/or and other determinations such as whether LCP 100 has become dislodged. In still some additional embodiments, LCP 100 may use the received information instead of the signals received from electrical sensing module 106 and/or mechanical sensing module 108—for instance if the received information is deemed to be more accurate than the signals received from electrical sensing module 106 and/or mechanical sensing module 108 or if electrical sensing module 106 and/or mechanical sensing module 108 have been disabled or omitted from LCP 100.

After determining an occurrence of an arrhythmia, processing module 110 may control pulse generator module 104 to generate electrical stimulation pulses in accordance with one or more electrical stimulation therapies to treat the determined arrhythmia. For example, processing module 110 may control pulse generator module 104 to generate pacing pulses with varying parameters and in different sequences to effectuate one or more electrical stimulation therapies. As one example, in controlling pulse generator module 104 to deliver bradycardia pacing therapy, processing module 110 may control pulse generator module 104 to deliver pacing pulses designed to capture the heart of the patient at a regular interval to help prevent the heart of a patient from falling below a predetermined threshold. In some cases, the rate of pacing may be increased with an increased activity level of the patient (e.g. rate adaptive pacing). For instance, processing module 110 may monitor one or more physiological parameters of the patient which may indicate a need for an increased heart rate (e.g. due to increased metabolic demand). Processing module 110 may then increase the rate at which pulse generator 104 generates electrical stimulation pulses.

For ATP therapy, processing module 110 may control pulse generator module 104 to deliver pacing pulses at a rate faster than an intrinsic heart rate of a patient in attempt to force the heart to beat in response to the delivered pacing pulses rather than in response to intrinsic cardiac electrical signals. Once the heart is following the pacing pulses, processing module 110 may control pulse generator module 104 to reduce the rate of delivered pacing pulses down to a safer level. In CRT, processing module 110 may control pulse generator module 104 to deliver pacing pulses in coordination with another device to cause the heart to contract more efficiently. In cases where pulse generator module 104 is capable of generating defibrillation and/or cardioversion pulses for defibrillation/cardioversion therapy, processing module 110 may control pulse generator module 104 to generate such defibrillation and/or cardioversion pulses. In some cases, processing module 110 may control pulse generator module 104 to generate electrical stimulation pulses to provide electrical stimulation therapies different than those examples described above.

Aside from controlling pulse generator module 104 to generate different types of electrical stimulation pulses and in different sequences, in some embodiments, processing module 110 may also control pulse generator module 104 to generate the various electrical stimulation pulses with varying pulse parameters. For example, each electrical stimulation pulse may have a pulse width and a pulse amplitude. Processing module 110 may control pulse generator module 104 to generate the various electrical stimulation pulses with specific pulse widths and pulse amplitudes. For example, processing module 110 may cause pulse generator module 104 to adjust the pulse width and/or the pulse amplitude of electrical stimulation pulses if the electrical stimulation pulses are not effectively capturing the heart. Such control of the specific parameters of the various electrical stimulation pulses may help LCP 100 provide more effective delivery of electrical stimulation therapy.

In some embodiments, processing module 110 may further control communication module 102 to send information to other devices. For example, processing module 110 may control communication module 102 to generate one or more communication signals for communicating with other devices of a system of devices. For instance, processing module 110 may control communication module 102 to generate communication signals in particular pulse sequences, where the specific sequences convey different information. Communication module 102 may also receive communication signals for potential action by processing module 110.

In further embodiments, processing module 110 may control switching circuitry by which communication module 102 and pulse generator module 104 deliver communication signals and/or electrical stimulation pulses to tissue of the patient. As described above, both communication module 102 and pulse generator module 104 may include circuitry for connecting one or more electrodes 114 and/114′ to communication module 102 and/or pulse generator module 104 so those modules may deliver the communication signals and electrical stimulation pulses to tissue of the patient. The specific combination of one or more electrodes by which communication module 102 and/or pulse generator module 104 deliver communication signals and electrical stimulation pulses may influence the reception of communication signals and/or the effectiveness of electrical stimulation pulses. Although it was described that each of communication module 102 and pulse generator module 104 may include switching circuitry, in some embodiments, LCP 100 may have a single switching module connected to the communication module 102, the pulse generator module 104, and electrodes 114 and/or 114′. In such embodiments, processing module 110 may control the switching module to connect modules 102/104 and electrodes 114/114′ as appropriate.

In some embodiments, processing module 110 may include a pre-programmed chip, such as a very-large-scale integration (VLSI) chip or an application specific integrated circuit (ASIC). In such embodiments, the chip may be pre-programmed with control logic in order to control the operation of LCP 100. By using a pre-programmed chip, processing module 110 may use less power than other programmable circuits while able to maintain basic functionality, thereby potentially increasing the battery life of LCP 100. In other instances, processing module 110 may include a programmable microprocessor or the like. Such a programmable microprocessor may allow a user to adjust the control logic of LCP 100 after manufacture, thereby allowing for greater flexibility of LCP 100 than when using a pre-programmed chip. In still other embodiments, processing module 110 may not be a single component. For example, processing module 110 may include multiple components positioned at disparate locations within LCP 100 in order to perform the various described functions. For example, certain functions may be performed in one component of processing module 110, while other functions are performed in a separate component of processing module 110.

Processing module 110, in additional embodiments, may include a memory circuit and processing module 110 may store information on and read information from the memory circuit. In other embodiments, LCP 100 may include a separate memory circuit (not shown) that is in communication with processing module 110, such that processing module 110 may read and write information to and from the separate memory circuit. The memory circuit, whether part of processing module 110 or separate from processing module 110, may be volatile memory, non-volatile memory, or a combination of volatile memory and non-volatile memory.

Energy storage module 112 may provide a power source to LCP 100 for its operations. In some embodiments, energy storage module 112 may be a non-rechargeable lithium-based battery. In other embodiments, the non-rechargeable battery may be made from other suitable materials. In some embodiments, energy storage module 112 may include a rechargeable battery. In still other embodiments, energy storage module 112 may include other types of energy storage devices such as capacitors or super capacitors.

To implant LCP 100 inside a patient's body, an operator (e.g., a physician, clinician, etc.), may fix LCP 100 to the cardiac tissue of the patient's heart. To facilitate fixation, LCP 100 may include one or more anchors 116. The one or more anchors 116 are shown schematically in FIG. 1. The one or more anchors 116 may include any number of fixation or anchoring mechanisms. For example, one or more anchors 116 may include one or more pins, staples, threads, screws, helix, tines, and/or the like. In some embodiments, although not shown, one or more anchors 116 may include threads on its external surface that may run along at least a partial length of an anchor member. The threads may provide friction between the cardiac tissue and the anchor to help fix the anchor member within the cardiac tissue. In some cases, the one or more anchors 116 may include an anchor member that has a cork-screw shape that can be screwed into the cardiac tissue. In other embodiments, anchor 116 may include other structures such as barbs, spikes, or the like to facilitate engagement with the surrounding cardiac tissue.

In some examples, LCP 100 may be configured to be implanted on a patient's heart or within a chamber of the patient's heart. For instance, LCP 100 may be implanted within any of a left atrium, right atrium, left ventricle, or right ventricle of a patient's heart. By being implanted within a specific chamber, LCP 100 may be able to sense cardiac electrical signals originating or emanating from the specific chamber that other devices may not be able to sense with such resolution. Where LCP 100 is configured to be implanted on a patient's heart, LCP 100 may be configured to be implanted on or adjacent to one of the chambers of the heart, or on or adjacent to a path along which intrinsically generated cardiac electrical signals generally follow. In these examples, LCP 100 may also have an enhanced ability to sense localized intrinsic cardiac electrical signals and deliver localized electrical stimulation therapy.

FIG. 2 depicts an embodiment of another device, medical device (MD) 200, which may operate to sense physiological signals and parameters and deliver one or more types of electrical stimulation therapy to tissues of the patient. In the embodiment shown, MD 200 may include a communication module 202, a pulse generator module 204, an electrical sensing module 206, a mechanical sensing module 208, a processing module 210, and an energy storage module 218. Each of modules 202, 204, 206, 208, and 210 may be similar to modules 102, 104, 106, 108, and 110 of LCP 100. Additionally, energy storage module 218 may be similar to energy storage module 112 of LCP 100. However, in some embodiments, MD 200 may have a larger volume within housing 220. In such embodiments, MD 200 may include a larger energy storage module 218 and/or a larger processing module 210 capable of handling more complex operations than processing module 110 of LCP 100.

While MD 200 may be another leadless device such as shown in FIG. 1, in some instances MD 200 may include leads, such as leads 212. Leads 212 may include electrical wires that conduct electrical signals between electrodes 214 and one or more modules located within housing 220. In some cases, leads 212 may be connected to and extend away from housing 220 of MD 200. In some embodiments, leads 212 are implanted on, within, or adjacent to a heart of a patient. Leads 212 may contain one or more electrodes 214 positioned at various locations on leads 212 and various distances from housing 220. Some leads 212 may only include a single electrode 214, while other leads 212 may include multiple electrodes 214. Generally, electrodes 214 are positioned on leads 212 such that when leads 212 are implanted within the patient, one or more of the electrodes 214 are positioned to perform a desired function. In some cases, the one or more of the electrodes 214 may be in contact with the patient's cardiac tissue. In other cases, the one or more of the electrodes 214 may be positioned subcutaneously but adjacent the patient's heart. The electrodes 214 may conduct intrinsically generated electrical cardiac signals to leads 212. Leads 212 may, in turn, conduct the received electrical cardiac signals to one or more of the modules 202, 204, 206, and 208 of MD 200. In some cases, MD 200 may generate electrical stimulation signals, and leads 212 may conduct the generated electrical stimulation signals to electrodes 214. Electrodes 214 may then conduct the electrical stimulation signals to the cardiac tissue of the patient (either directly or indirectly). MD 200 may also include one or more electrodes 214 not disposed on a lead 212. For example, one or more electrodes 214 may be connected directly to housing 220.

Leads 212, in some embodiments, may additionally contain one or more sensors, such as accelerometers, blood pressure sensors, heart sound sensors, blood-oxygen sensors, and/or other sensors which are configured to measure one or more physiological parameters of the heart and/or patient. In such embodiments, mechanical sensing module 208 may be in electrical communication with leads 212 and may receive signals generated from such sensors.

While not required, in some embodiments MD 200 may be an implantable medical device. In such embodiments, housing 220 of MD 200 may be implanted in, for example, a transthoracic region of the patient. Housing 220 may generally include any of a number of known materials that are safe for implantation in a human body and may, when implanted, hermetically seal the various components of MD 200 from fluids and tissues of the patient's body. In such embodiments, leads 212 may be implanted at one or more various locations within the patient, such as within the heart of the patient, adjacent to the heart of the patient, adjacent to the spine of the patient, or any other desired location.

In some embodiments, MD 200 may be an implantable cardiac pacemaker (ICP). In these embodiments, MD 200 may have one or more leads, for example leads 212, which are implanted on or within the patient's heart. The one or more leads 212 may include one or more electrodes 214 that are in contact with cardiac tissue and/or blood of the patient's heart. MD 200 may be configured to sense intrinsically generated cardiac electrical signals and determine, for example, one or more cardiac arrhythmias based on analysis of the sensed signals. MD 200 may be configured to deliver CRT, ATP therapy, bradycardia therapy, and/or other therapy types via leads 212 implanted within the heart. In some embodiments, MD 200 may additionally be configured to provide defibrillation/cardioversion therapy.

In some instances, MD 200 may be an implantable cardioverter-defibrillator (ICD). In such embodiments, MD 200 may include one or more leads implanted within a patient's heart. MD 200 may also be configured to sense electrical cardiac signals, determine occurrences of tachyarrhythmias based on the sensed electrical cardiac signals, and deliver defibrillation and/or cardioversion therapy in response to determining an occurrence of a tachyarrhythmia (for example by delivering defibrillation and/or cardioversion pulses to the heart of the patient). In other embodiments, MD 200 may be a subcutaneous implantable cardioverter-defibrillator (SICD). In embodiments where MD 200 is an SICD, one of leads 212 may be a subcutaneously implanted lead. In at least some embodiments where MD 200 is an SICD, MD 200 may include only a single lead which is implanted subcutaneously but outside of the chest cavity, however this is not required.

In some embodiments, MD 200 may not be an implantable medical device. Rather, MD 200 may be a device external to the patient's body, and electrodes 214 may be skin-electrodes that are placed on a patient's body. In such embodiments, MD 200 may be able to sense surface electrical signals (e.g. electrical cardiac signals that are generated by the heart or electrical signals generated by a device implanted within a patient's body and conducted through the body to the skin). MD 200 may further be configured to deliver various types of electrical stimulation therapy, including, for example, defibrillation therapy via skin-electrodes 214.

FIG. 3 illustrates an embodiment of a medical device system and a communication pathway through which multiple medical devices 302, 304, 306, and/or 310 of the medical device system may communicate. In the embodiment shown, medical device system 300 may include LCPs 302 and 304, external medical device 306, and other sensors/devices 310. External device 306 may be a device disposed external to a patient's body, as described previously with respect to MD 200. In at least some examples, external device 306 may represent an external support device such as a device programmer, as will be described in more detail below. Other sensors/devices 310 may be any of the devices described previously with respect to MD 200, such as ICPs, ICDs, and SICDs. Other sensors/devices 310 may also include various diagnostic sensors that gather information about the patient, such as accelerometers, blood pressure sensors, or the like. In some cases, other sensors/devices 310 may include an external programmer device that may be used to program one or more devices of system 300.

Various devices of system 300 may communicate via communication pathway 308. For example, LCPs 302 and/or 304 may sense intrinsic cardiac electrical signals and may communicate such signals to one or more other devices 302/304, 306, and 310 of system 300 via communication pathway 308. In one embodiment, one or more of devices 302/304 may receive such signals and, based on the received signals, determine an occurrence of an arrhythmia. In some cases, device or devices 302/304 may communicate such determinations to one or more other devices 306 and 310 of system 300. In some cases, one or more of devices 302/304, 306, and 310 of system 300 may take action based on the communicated determination of an arrhythmia, such as by delivering a suitable electrical stimulation to the heart of the patient. One or more of devices 302/304, 306, and 310 of system 300 may additionally communicate command or response messages via communication pathway 308. The command messages may cause a receiving device to take a particular action whereas response messages may include requested information or a confirmation that a receiving device did, in fact, receive a communicated message or data.

It is contemplated that the various devices of system 300 may communicate via pathway 308 using RF signals, inductive coupling, optical signals, acoustic signals, or any other signals suitable for communication. Additionally, in at least some embodiments, the various devices of system 300 may communicate via pathway 308 using multiple signal types. For instance, other sensors/device 310 may communicate with external device 306 using a first signal type (e.g. RF communication) but communicate with LCPs 302/304 using a second signal type (e.g. conducted communication). Further, in some embodiments, communication between devices may be limited. For instance, as described above, in some embodiments, LCPs 302/304 may communicate with external device 306 only through other sensors/devices 310, where LCPs 302/304 send signals to other sensors/devices 310, and other sensors/devices 310 relay the received signals to external device 306.

In some cases, the various devices of system 300 may communicate via pathway 308 using conducted communication signals. Accordingly, devices of system 300 may have components that allow for such conducted communication. For instance, the devices of system 300 may be configured to transmit conducted communication signals (e.g. a voltage and/or current waveform punctuated with current and/or voltage pulses, referred herein as electrical communication pulses) into the patient's body via one or more electrodes of a transmitting device, and may receive the conducted communication signals via one or more electrodes of a receiving device. The patient's body may “conduct” the conducted communication signals from the one or more electrodes of the transmitting device to the electrodes of the receiving device in the system 300. In such embodiments, the delivered conducted communication signals may differ from pacing pulses, defibrillation and/or cardioversion pulses, or other electrical stimulation therapy signals. For example, the devices of system 300 may deliver electrical communication pulses at an amplitude/pulse width that is sub-threshold. That is, the communication pulses have an amplitude/pulse width designed to not capture the heart. In some cases, the amplitude/pulse width of the delivered electrical communication pulses may be above the capture threshold of the heart, but may be delivered during a refractory period of the heart and/or may be incorporated in or modulated onto a pacing pulse, if desired.

Additionally, unlike normal electrical stimulation therapy pulses, the electrical communication pulses may be delivered in specific sequences which convey information to receiving devices. For instance, delivered electrical communication pulses may be modulated in any suitable manner to encode communicated information. In some cases, the communication pulses may be pulse width modulated and/or amplitude modulated. Alternatively, or in addition, the time between pulses may be modulated to encode desired information. In some cases, a predefined sequence of communication pulses may represent a corresponding symbol (e.g. a logic “1” symbol, a logic “0” symbol, an ATP therapy trigger symbol, etc.). In some cases, conducted communication pulses may be voltage pulses, current pulses, biphasic voltage pulses, biphasic current pulses, or any other suitable electrical pulse as desired.

FIG. 4 depicts an illustrative medical device system 400 that may be configured to operate together. For example, system 400 may include multiple devices that are implanted within a patient and are configured to sense physiological signals, determine occurrences of cardiac arrhythmias, and deliver electrical stimulation to treat detected cardiac arrhythmias. In some embodiments, the devices of system 400 may be configured to determine occurrences of dislodgment of one or more devices of system 400. In FIG. 4, an LCP 402 is shown fixed to the interior of the right ventricle of the heart 410, and a pulse generator 406 is shown coupled to a lead 412 having one or more electrodes 408 a-408 c. In some cases, pulse generator 406 may be part of a subcutaneous implantable cardioverter-defibrillator (SICD), and the one or more electrodes 408 a-408 c may be positioned subcutaneously adjacent the heart. LCP 402 may communicate with the SICD, such as via communication pathway 308. The locations of LCP 402, pulse generator 406, lead 412, and electrodes 408 a-c depicted in FIG. 4 are just exemplary. In other embodiments of system 400, LCP 402 may be positioned in the left ventricle, right atrium, or left atrium of the heart, as desired. In still other embodiments, LCP 402 may be implanted externally adjacent to heart 410 or even remote from heart 410.

Medical device system 400 may also include external support device 420. External support device 420 can be used to perform functions such as device identification, device programming and/or transfer of real-time and/or stored data between devices using one or more of the communication techniques described herein, or other functions involving communication with one or more devices of system 400. As one example, communication between external support device 420 and pulse generator 406 can be performed via a wireless mode, and communication between pulse generator 406 and LCP 402 can be performed via a conducted communication mode. In some embodiments, communication between LCP 402 and external support device 420 is accomplished by sending communication information through pulse generator 406. However, in other embodiments, communication between the LCP 402 and external support device 420 may be via a communication module.

FIG. 4 only illustrates one example embodiment of a medical device system that may be configured to operate according to techniques disclosed herein. Other example medical device systems may include additional or different medical devices and/or configurations. For instance, other medical device systems that are suitable to operate according to techniques disclosed herein may include additional LCPs implanted within the heart. Another example medical device system may include a plurality of LCPs with or without other devices such as pulse generator 406, with at least one LCP capable of delivering defibrillation therapy. Still another example may include one or more LCPs implanted along with a transvenous pacemaker and with or without an implanted SICD. In yet other embodiments, the configuration or placement of the medical devices, leads, and/or electrodes may be different from those depicted in FIG. 4. Accordingly, it should be recognized that numerous other medical device systems, different from system 400 depicted in FIG. 4, may be operated in accordance with techniques disclosed herein. As such, the embodiment shown in FIG. 4 should not be viewed as limiting in any way.

In some embodiments, LCP 100 may be configured to determine whether a tamponade condition is occurring. For instance, LCP 100 may be configured to monitor one or more signals and determine, based on the one or more monitored signals, whether a tamponade condition is occurring within the heart. Additionally, or alternatively, LCP 100 may use one or more determined features or characteristics of the monitored signal or signals and determine whether tamponade is occurring based on the one or more determined features. In some embodiments, to determine whether a tamponade condition is occurring, LCP 100 may monitor a signal or a feature of the signal and determine whether the signal or the feature changes (e.g. diminishes) over time. Generally, diminishment of a signal or feature over time, such as diminishing below a threshold, may indicate that a tamponade condition is occurring. The below described techniques illustrate various signals and features that LCP 100 may monitor in order to determine whether a tamponade condition is occurring. In some cases, the LCP 100 may monitor one or more signals or features, and communicate information related to the one or more signals or features to a separate device. In some cases, the actual determination of whether a tamponade condition is occurring may be performed by the separate device.

In some embodiments, LCP 100 may be triggered to enter or exit a tamponade mode, where LCP 100 monitors for whether a tamponade condition is occurring. In some cases, the LCP may enter or exit the tamponade mode based on a communicated trigger signal. LCP 100 may receive such a trigger signal from a device external to LCP 100, such as support device 420, or may be internally generated. Generally, a user may trigger LCP 100, e.g. via external support device 420, to enter the tamponade mode at the time of implant and maintain LCP 100 in the tamponade mode throughout the implantation procedure and for a short time thereafter. A user may additionally trigger LCP 100 to enter the tamponade mode during follow-up procedures or appointments where the physician may be concerned that tamponade is a risk. Outside of these times, the physician may trigger tamponade detection off to save energy in the LCP.

FIG. 5 is a graph 500 showing an illustrative cardiac electrical signal 502 (e.g. ECG) along with corresponding accelerometer signals 504, 506, 508 and 510 of a three axis accelerometer along a common time axis. The signal tracings of graph 500 may represent signals sensed or generated by an LCP 100 when LCP 100 is attached to a wall of a patients' heart. For example, signal 502 may represent a cardiac electrical signal 502 sensed by LCP 100. Signals 504, 506, and 508 may represent signals from different axes generated by a three-axis accelerometer of LCP 100. Signal 510 may represent an accelerometer magnitude signal, which may be determined by summing signals 504, 506, and 508 or summing the absolute values of signals 504, 506, and 508. In other embodiments, signal 510 may represent a different signal generated by other combinations of signals 504, 506, and 508, such as a root-mean-square or root-sum-square of signals 504, 506, and 508, or any other derivation of signals 504, 506, and 508.

LCP 100 may be configured to sense one or more of signals 504, 506, 508 and/or 510 during certain time periods. For instance, to “sense” one or more of the signals, it is contemplated that the LCP 100 may be configured to receive and process signals 504, 506, 508 and/or 510 at processing module 110. Whereas when the one or more of the signals are not being “sensed”, processing module 110 of LCP 100 may not receive and/or process the signals 504, 506, 508 and/or 510. In some embodiments, to “sense” signals 504, 506, 508 and/or 510, LCP 100 may connect an output of the accelerometer to processing module 110 via a switch, multiplexer of the like. In other embodiments, the accelerometer may be configured to only output valid signals 504, 506, 508 and/or 510 when the accelerometer is to be sensed (e.g. the accelerometer may be enabled by processing module 110 when sensing is desired). In some cases, LCP 100 may control the generation of signals 504, 506, 508 and/or 510 by the accelerometer. For instance, LCP 100 may control when power is provided to the accelerometer, and the accelerometer may only generate signals 504, 506, 508 and/or 510 when power is provided to the accelerometer. In some cases, LCP 100 may switch the accelerometer from a lower-power state (e.g. a sleep mode) to a higher-power state (e.g. awake or active mode) during time periods where LCP 100 is to sense the accelerometer signal(s). During the lower-power state, the accelerometer may not provide an appreciable signal for LCP 100 to sense and/or sample. In some cases, and where processing module 110 is a digital device, an A/D converter may sample signals 504, 506, 508 and/or 510 when sensing is desired. These are just some examples of how signals 504, 506, 508 and/or 510 may be “sensed” during certain time periods.

LCP 100 may be configured to sense one or more signals during predetermined time periods. Such predetermined time periods may be represented by sensing periods 512 a-512 d in FIG. 5. Sensing periods 512 a-512 d may occur at regular intervals, such as every five seconds, every second, every eight hundred milliseconds, every seven hundred milliseconds, or any other suitable value. Alternatively, LCP 100 may initiate sensing periods 512 a-512 d after every beat, once every other beat, once every five beats, or at any other suitable frequency and/or duration. In at least some cases, LCP 100 may adjust the interval according to a heart rate of the patient such that successive sensing periods 512 a-512 d occur during the same portion of the cardiac cycle (e.g. when the heart is quiet such as between heart beats).

In some instances, LCP 100 may implement sensing periods 512 a-512 d based on one or more detected features of cardiac electrical signal 502. For instance, LCP 100 may detect one or more features of cardiac electrical signal 502, such as cardiac electrical events 511. Cardiac electrical events 511 may represent R-waves or other morphological features detected by LCP 100. Upon detection of cardiac electrical event 511, LCP 100 may initiate a time delay, such as time delay 514. Upon expiration of time delay 514, LCP 100 may initiate sensing periods 512 a-512 d, during which LCP 100 may “sense” one or more signals, such as signals 504, 506, 508 and/or 510. In at least some cases, LCP 100 may adjust time delay 514 based on the heart rate of the patient. For instance, when the heart rate is at a relatively higher heart rate, LCP 100 may shorten time delay 514, and when the heart rate is at a relatively lower heart rate, LCP 100 may lengthen time delay 514. This may help the LCP 100 consistently initiate sensing periods 512 a-512 d during the same or similar portion of the cardiac cycle (e.g. during the quit period between polarization/repolarizations of the heart).

In some instances, the length of time delay 514 may be chosen to align with a portion of the cardiac cycle where the heart is relatively mechanically inactive, such as shown in FIG. 5. For instance, time delay 514 may be chosen so that it expires between about fifty milliseconds to about one-hundred fifty milliseconds before the beginning of the next heartbeat. During this portion of the cardiac cycle, the heart muscle may be in a relatively relaxed state while filling with blood. Accordingly, during this portion of the cardiac cycle, the orientation of LCP 100 may be at a relatively consistent position. This may allow LCP 100 to more easily detect a current posture of the patient, as explained in more detail below. In other embodiments, an accelerometer or other sensor may be implanted in the patient outside of the heart, and may transmit an indication of posture to the LCP 100.

The signals depicted in FIG. 5 may represent signals acquired during normal cardiac function, e.g. when no tamponade condition is occurring. Notice that each of the accelerometer signals following each cardiac electrical event 511 are similar in shape and magnitude.

FIG. 6 depicts graph 520 including an example cardiac electrical signal 522, including cardiac electrical events 531, and accelerometer signal 524 which represents a magnitude of the accelerometer of LCP 100, similar to signal 510 of FIG. 5. Graph 520 depicts signals 522 and 524 over multiple cardiac cycles where the patient is suffering from a tamponade condition. As can be seen in FIG. 6, the maximum amplitude of signal 524 diminishes over time throughout successive cardiac cycles. However, the maximum amplitude of the illustrative cardiac electrical signal 522 remains relatively constant over the same cardiac cycles. Accordingly, detecting a tamponade condition may be difficult using only the cardiac electrical signal.

While FIG. 6 shows the maximum amplitude of signal 524 diminish rapidly over only five (5) cardiac cycles, this has been intentionally compressed in time for ease of description only. In most cases, the maximum amplitude of signal 524 will diminish much more slowly, such as over minutes, hours or even days. FIGS. 7-9 have been similarly compressed in time for ease of description.

When LCP 100 is in the tamponade mode, LCP 100 may adjust how LCP 100 senses the accelerometer signal(s). As can be seen, time delay 526 of FIG. 6 is relatively shorter than time delay 514 of FIG. 5. The length of time delay 526 may be chosen to generally align with the contraction of the heart. This may help LCP 100 sense the accelerometer signals during sensing periods 523 a-e that correspond to when the heart is actually contracting.

In some instances, time delay 526 may be about ten milliseconds, about fifteen milliseconds, about twenty milliseconds, about twenty-five milliseconds, about thirty milliseconds, about thirty-five milliseconds, or any other suitable period of time following a detected R-wave. In general, time delay 526 may have a value that is less than an electromechanical delay of the heart, which is the delay between when LCP 100 detects a cardiac electrical event 531 (e.g. R-wave) and an onset of cardiac wall motion or a threshold amount of cardiac wall motion. Sensing periods 523 a-e may have a duration of about twenty-five milliseconds, about thirty milliseconds, about forty milliseconds, or about fifty milliseconds. However, in other embodiments, sensing periods 523 a-e may be substantially longer, for instance, about half of a cardiac cycle of the patient, about three quarters of the cardiac cycle of the patient, or may span an entire cardiac cycle of the patient. In some additional or alternative embodiments, time delay 526 and/or sensing periods 523 a-e may have lengths that change along with the heart rate of the patient. As one example, for relatively higher heart rates, time delay 526 and/or sensing periods 523 a-e may be shorter than for relatively lower heart rates.

In general, LCP 100 may be able to use accelerometer signals sensed during a portion of the cardiac cycle that corresponds to sensing periods 523 a-e to determine whether a tamponade condition is occurring. As mentioned previously, when tamponade is occurring, blood or other fluid may be pooling in the pericardial sac, preventing full relaxation of the heart between contractions. The pooled blood may then prevent the heart from contracting to as great of an extent as under normal conditions. This difference in the motion of the heart may be seen through the sensed accelerometer signals.

To determine whether a tamponade condition is occurring, in some instances, LCP 100 may compare a maximum amplitude of signal 524 within a sensing window to a threshold, such as threshold 525. If LCP 100 determines that the maximum amplitude of signal 524 is less than threshold 525, LCP 100 may determine that a tamponade condition is occurring. In other embodiments, after determining that the maximum amplitude of signal 524 is less than threshold 525 in a first sensing window, such as sensing window 523 c, LCP 100 may continue to monitor signal 524 during subsequent sensing windows, for example sensing windows 523 d and 523 e, and comparing signal 524 to threshold 525 during those subsequent sensing windows. In these embodiments, LCP 100 may only determine that a tamponade condition is occurring if the maximum amplitude of signal 524 in a second, subsequent sensing window is also less than threshold 525. In still further embodiments, LCP 100 may require the maximum amplitude of signal 524 to be less than threshold 525 in three (or more) consecutive sensing windows before determining that a tamponade condition is occurring.

In still other embodiments, LCP 100 may require the maximum amplitude of signal 524 to be less than threshold 525 in four, five, ten, or twenty consecutive sensing windows, or any other suitable number of sensing windows, before determining that a tamponade condition is occurring. Other options further include LCP 100 requiring that the maximum amplitude of signal 524 to be less than threshold 525 in three out of five consecutive sensing windows, five out of ten consecutive sensing windows, or any other suitable combinations before determining that a tamponade condition is occurring.

In even more additional or alternative embodiments, after LCP 100 determines the maximum amplitude of signal 524 is less than threshold 525, LCP 100 may track a period of time. LCP 100 may then determine that a tamponade condition is occurring if the maximum amplitude of signal 524 does not cross back above threshold 525 within the predefined period of time. In some instances, LCP 100 may switch to continuously or substantially continuously sensing signal 524 (e.g. turn on and/or sample accelerometer signal continuously or substantially continuously). In other embodiments, however, LCP 100 may maintain sensing signal 524 only in sensing windows. Accordingly, rather than counting a number of sensing windows, LCP 100 may simply monitor signal 524 within any number of subsequent sensing windows which fall within the tracked period of time

In other alternative embodiments, LCP 100 may track a moving average of the maximum amplitude of signal 524 over about three, about five, about ten, about fifteen, or about twenty cardiac cycles, or any other suitable number of cardiac cycles, and may store the determined moving averages in a memory. During a tamponade condition, this moving average will steadily decrease over time as the heart loses its ability to expand and pump blood due to blood pooling in the pericardial sac. Accordingly, in some embodiments, LCP 100 may compare the moving average to a threshold to determine whether a tamponade condition is occurring. In other or additional embodiments, LCP 100 may determine whether the stored moving averages decrease in a monotonic fashion. If LCP 100 determines that about five, about ten, about fifteen, or any other suitable number of consecutive determined moving averages decrease in a monotonic fashion, LCP 100 may determine that a tamponade condition is occurring.

Alternatively, LCP 100 may determine the slopes between consecutive determined moving averages. If LCP 100 determines that a threshold number, such as three, five, ten, fifteen, or twenty, of consecutive slopes are negative, LCP 100 may determine that a tamponade condition is occurring. Also, the magnitude of the slope(s) may be taken into consideration. A larger slope may indicate a more severe tamponade condition, and thus the LCP 100 may determine that a tamponade condition is occurring sooner.

Although the above tamponade detection techniques included monitoring for tamponade over a relatively short time period, e.g. a number of cardiac cycles, in some additional or alternative embodiments, LCP 100 may be configured to monitor for a tamponade condition over longer periods of time. For instance, LCP 100 may be configured to monitor for tamponade once an hour, once every few hours, twice a day, or once a day. In these embodiments, LCP 100 may monitor, for example, the maximum amplitude of signal 524 during one or more sensing periods during each chosen time interval. LCP 100 may then compare the sensed maximum amplitude of signal 524 during each of these chosen time intervals to determine if there is a trend. For example, LCP 100 may compare these determined differences to one or more thresholds, as above, to determine if a tamponade condition is occurring. This may facilitate detection of slow-onset tamponade conditions.

FIG. 7 depicts another embodiment where LCP 100 may be configured to determine that a tamponade condition is occurring. FIG. 7 depicts a graph 540 showing an accelerometer signal 542, which may represent a magnitude of acceleration from an accelerometer of LCP 100. In the example of FIG. 7, LCP 100 may employ multiple thresholds in determining whether a tamponade condition is occurring. For example, LCP 100 may initially monitor accelerometer signal 542 during sensing windows 541 a-541 e to determine when a maximum amplitude of signal 542 within a sensing window falls below first threshold 543. Once LCP 100 determines that signal 542 has fallen below first threshold 543, LCP 100 may monitor accelerometer signal 542 to determine if, or when, accelerometer signal 542 falls below second threshold 545. In the example of FIG. 7, LCP 100 would determine that accelerometer signal 542 falls below second threshold 545 in the next sensing window 541 d. At this point, after accelerometer signal 542 has fallen below the first threshold 543 and then subsequently fallen below the second threshold 545, LCP 100 may determine that a tamponade condition is occurring, as this trend may indicate declining mechanical motion of the heart. Of course, in additional embodiments, LCP 100 may only determine that a tamponade condition is occurring after determining that a maximum amplitude of accelerometer signal 542 in multiple subsequent sensing windows is still below second threshold 545, for instance in any manner that was described with respect to FIG. 6.

Of course, in some cases, the maximum amplitude of accelerometer signal 542 may be above both first threshold 543 and second threshold 545 in a first sensing window and may be less than both first threshold 543 and second threshold 545 in a next sensing window. In such embodiments, LCP 100 may monitor subsequent sensing windows and determine whether the maximum amplitude of accelerometer signal 542 stays below second threshold 545. If LCP 100 determines the maximum amplitude of accelerometer signal 542 stays below second threshold 545 for one or more subsequent sensing windows, LCP 100 may then determine that a tamponade condition is occurring. In such embodiments, the tamponade condition may worsen too quickly for LCP 100 to sense the decline in mechanical motion of the heart, and LCP 100 may instead rely simply on a consistent indication of low cardiac motion to determine that a tamponade condition is occurring.

In some embodiments, first threshold 543 may be set as a certain percentage of a maximum value of sensed signal 542 in a sensing window when signal 542 is sensed under conditions where it is known that tamponade is not occurring. For instance, first threshold 543 may be set at about seventy-five percent of the maximum value of sensed signal 542 in a sensing window. However, in other embodiments, first threshold 543 may be set at different percentages of the maximum value of sensed signal 542 in a sensing window, such as about fifty percent, about sixty-percent, about seventy percent, about eighty percent, about eighty-five percent, about ninety percent, or any other suitable value. In some embodiments, the value of second threshold 543 may be programmable.

Second threshold 545 may be set at a certain percentage of first threshold 543. For instance, second threshold 545 may be set at about seventy-five percent of first threshold 543. However, in other embodiments, second threshold 545 may be set at different percentages of first threshold 543, such as about fifty percent, about sixty-percent, about seventy percent, about eighty percent, about eighty-five percent, about ninety percent, or any other suitable value. In some embodiments, the value of second threshold 545 may be programmable.

FIG. 8 depicts still another embodiment where LCP 100 may be configured to determine that a tamponade condition is occurring. FIG. 8 depicts a graph 550 showing an accelerometer signal 552, which may represent a magnitude of acceleration from an accelerometer of LCP 100. In the example of FIG. 8, LCP 100 may employ multiple thresholds in determining whether a tamponade condition is occurring. For example, LCP 100 may initially monitor accelerometer signal 552 during sensing windows 551 a-551 e to determine when a maximum amplitude of accelerometer signal 552 within a sensing window falls below first threshold 553.

Once LCP 100 determines that the maximum amplitude of signal 552 has fallen below first threshold 553, such as in sensing window 551 c, LCP 100 may monitor accelerometer signal 552 to determine if, or when, accelerometer signal 552 rises above second threshold 555. For example, LCP 100 may monitor accelerometer signal 552 for a number of subsequent sensing windows, or for a predefined period of time, after detecting that the maximum amplitude of accelerometer signal 552 is less than first threshold 553. If LCP 100 determines that the maximum amplitude of accelerometer signal 552 did not rise above second threshold 555 within the predetermined number of subsequent sensing windows, or within the predefined period of time, LCP 100 may determine that a tamponade condition is occurring. If LCP 100 determines that accelerometer signal 552 did rise above second threshold 555 within the predetermined number of subsequent sensing windows, or within the predefined period of time, LCP 100 may then switch back to monitoring whether the maximum amplitude of accelerometer signal 552 is below first threshold 553.

In some embodiments, first threshold 553 may be set as a certain percentage of a maximum value of sensed signal 552 in a sensing window when signal 552 is sensed under conditions where it is known that tamponade is not occurring. For instance, first threshold 553 may be set at about seventy-five percent of the maximum value of sensed signal 552 in a sensing window. However, in other embodiments, first threshold 553 may be set at different percentages of the maximum value of sensed signal 552 in a sensing window, such as about fifty percent, about sixty-percent, about seventy percent, about eighty percent, about eighty-five percent, about ninety percent, or any other suitable value. In some embodiments, the value of second threshold 553 may be programmable.

Second threshold 555 may be may be set at a certain percentage of first threshold 543. For instance, second threshold 545 may be set at about seventy-five percent of first threshold 543. However, in other embodiments, second threshold 545 may be set at different percentages of first threshold 543, such as about fifty percent, about sixty-percent, about seventy percent, about eighty percent, about eighty-five percent, about ninety percent, or any other suitable value. In some embodiments, the value of second threshold 555 may be programmable.

FIG. 9 depicts still another embodiment where LCP 100 may be configured to determine that a tamponade condition is occurring. FIG. 9 depicts a graph 560 showing an accelerometer signal 562, which may represent a magnitude of acceleration from an accelerometer of LCP 100. In the example of FIG. 9, LCP 100 may employ multiple thresholds in determining whether a tamponade condition is occurring. For example, LCP 100 may initially monitor accelerometer signal 562 during sensing windows 561 a-561 e to determine when a maximum amplitude of accelerometer signal 562 within a sensing window falls below first threshold 563.

Once LCP 100 determines that the maximum amplitude of accelerometer signal 562 has fallen below first threshold 563, such as in sensing window 561 c, LCP 100 may monitor accelerometer signal 562 to determine whether accelerometer signal 562 falls below second threshold 565 or rises above third threshold 567. For example, LCP 100 may monitor accelerometer signal 562 for a number of subsequent sensing windows, or for a predefined period of time, after detecting that the maximum amplitude of accelerometer signal 562 is less than first threshold 563. If LCP 100 determines that the maximum amplitude of accelerometer signal 562 rises above third threshold 567 before falling below second threshold 565, LCP 100 may go back to determining whether the maximum amplitude of accelerometer signal 562 is below first threshold 563. However, if LCP 100 determine that the maximum amplitude of accelerometer signal 562 does not rise above third threshold 567 within the predetermined number of subsequent sensing windows, or for the predefined period of time, LCP 100 may determine that a tamponade condition is occurring. Additionally, if LCP 100 determines that the maximum amplitude of accelerometer signal 562 falls below second threshold 565 at any point, LCP 100 may determine a tamponade condition is occurring, even if the predetermined number of subsequent sensing windows have not occurred, or the predefined period of time ran out.

In some embodiments, first threshold 563 may be set as a certain percentage of a maximum value of sensed signal 562 in a sensing window when signal 562 is sensed under conditions where it is known that tamponade is not occurring. For instance, first threshold 563 may be set at about seventy-five percent of the maximum value of sensed signal 562 in a sensing window. However, in other embodiments, first threshold 563 may be set at different percentages of the maximum value of sensed signal 562 in a sensing window, such as about fifty percent, about sixty-percent, about seventy percent, about eighty percent, about eighty-five percent, about ninety percent, or any other suitable value. In some embodiments, the value of second threshold 563 may be programmable.

Second threshold 565 and/or third threshold 567 may be set at a certain percentage of first threshold 563. For instance, third threshold 567 may be set at about seventy-five percent of first threshold 563. However, in other embodiments, third threshold 567 may be set at different percentages of first threshold 563, such as about fifty percent, about sixty-percent, about seventy percent, about eighty percent, about eighty-five percent, about ninety percent, or any other suitable value. In some embodiments, second threshold 565 may be set at about fifty percent of first threshold 563. However, in other embodiments, second threshold 565 may be set at different percentages of first threshold 563, such as about twenty-five percent, about thirty percent, about thirty-five percent, about forty percent, about forty-five percent, or any other suitable value. In some embodiments, the value of second and/or third threshold 565, 567 may be programmable.

Although the embodiments of FIGS. 6-9 all use the magnitude of the accelerometer signal, it should be understood that this is for illustrative purposes only. In other embodiments, LCP 100 may use other signals to determine whether a tamponade condition is occurring. For example, LCP 100 may use any signal received from the accelerometer, such as the different signals representing different axes of the accelerometer, to determine whether a tamponade condition is occurring. LCP 100 may further process the accelerometer signal to derive one or more other signals for use in determining whether a tamponade condition is occurring. As one example, LCP 100 may double integrate the accelerometer signal to determine a displacement signal, representing the displacement of the accelerometer over time, which correlates to displacement of the heart wall. LCP 100 may compare a maximum amplitude of a portion of this displacement signal, such as during a filling of the heart, to one or more thresholds to determine whether a tamponade condition is occurring. For instance, the maximum amplitude of the displacement signal in the monitored portion may relate to the amount of movement of the cardiac wall during filling. As blood pools in the pericardial sac, the maximum value of this signal will decrease over time. Accordingly, LCP 100 may monitor whether this value decreases below one or more threshold and, if so, determine an occurrence of a tamponade condition. Like with the accelerometer signal, LCP 100 may use a feature of the cardiac electrical signal to determine which portion of the displacement signal to monitor. For instance, LCP 100 may track a period of time from a cardiac electrical event and begin monitoring the displacement signal for the maximum amplitude within a sensing window beginning upon expiration of the period of time. In at least some embodiments, the period of time used for the accelerometer signal and the period of time used for the displacement signal are different.

In still other embodiments, LCP 100 may include other sensors and may use signals from those sensors to determine whether a tamponade condition is occurring. Some other example sensors include a pressure sensor and/or a gyroscope. When provided, a gyroscope may be a multi-axis gyroscope and generate signals similar to the multi-axis accelerometer described above. In some cases, as mentioned previously, signals generated by a gyroscope may have a certain synchrony with the cardiac electrical signals which may change during a tamponade condition. Loss of the synchrony of a peak value of the gyroscope signal and the cardiac electrical events may indicate a tamponade condition is occurring. In other embodiments, LCP 100 may employ any of the techniques described with respect to the accelerometer signal to the gyroscope signal to determine whether a tamponade condition is occurring.

Further, as a tamponade condition is worsening, the intra-chamber blood pressure, and in particular the intra-chamber blood pressure as the heart contracts to pump the blood, may change over time in a diminishing manner. In these embodiments, LCP 100 may monitor an intra-chamber blood pressure signal detected via a pressure sensor and/or detected via heart sounds via an accelerometer or the like. For example, the amplitude of the first heart sound (51), which can be detected by an accelerometer or the like, is proportional to the rate of left ventricular pressure rise (LV dP/dt). LCP 100 may compare a maximum amplitudes of this blood pressure signal taken over time to one or more thresholds. In general, any of the threshold techniques described above with respect to the maximum amplitude of the accelerometer may be applied to the blood pressure signal.

In some further embodiments, LCP 100 may monitor a time duration of the peak of the dP/dt signal, such as by monitoring how long the dP/dt signal stays within a certain percentage of the peak dP/dt signal value over a cardiac cycle, such as within about three percent, about five percent, about eight percent, or about ten percent. During a tamponade condition, this time value may lengthen. Accordingly, LCP 100 may compare this determined time value to a threshold, and LCP 100 may determine that a tamponade condition is occurring if the value rises above a threshold.

In still other embodiments, LCP 100 may monitor heart sounds for indications of valve closures, for instance based on deflections in the heart sounds signal. If LCP 100 determines that there is a lack of detected expected valve closures, LCP 100 may determine an occurrence of a tamponade condition. For instance, LCP 100 may expect to detect two, three, or four heart sound features in the heart sounds signal for each cardiac cycle. If LCP 100 detects less than is expected, LCP 100 may determine that a tamponade condition is occurring. Additionally, or alternatively, LCP 100 may determine that a tamponade condition is occurring if a monitored maximum amplitude of the heart sounds signal falls below a threshold for one or more cardiac cycles, or the heart sounds signal differs from a template heart sounds signal.

Accordingly, in any these above embodiments, instead of using signals from an accelerometer, LCP 100 may use signals from the gyroscope, the blood pressure sensors, or any other sensors in any manner described above to determine whether a tamponade condition is occurring.

In still other embodiments, LCP 100 may use multiple signals to determine whether tamponade is occurring. For instance, LCP 100 may perform analyses on multiple signals generated by the accelerometer, gyroscope, and/or blood pressure sensor. In some of these embodiments, LCP 100 may determine that a tamponade condition is occurring if analysis on any one signal indicates a tamponade condition. However, in other embodiments, LCP 100 may only determine that a tamponade condition is occurring if multiple of the signals indicate a tamponade condition, such as two signals, three signals, four signals, all of the signals, or any other suitable number of signals.

Where LCP 100 uses multiple signals to determine whether tamponade is occurring, LCP 100 may, in some examples, analyze the signals in a cascading fashion. For instance, LCP 100 may initially only monitor a single signal. After determining that the first signal indicates that a tamponade condition is occurring, LCP 100 may then begin to monitor a second signal. In some instances, only after the second signal has indicated that a tamponade condition is occurring does the LCP 100 determine that a tamponade condition is occurring. In some cases, LCP 100 may be able to cascade the analysis of the signals in order to save energy. For instance, in some embodiments LCP 100 may be configured to monitor a first signal from an accelerometer while the other channels of the accelerometer or other sensors are turned off. Only after the first accelerometer signal indicates that a tamponade condition is occurring does the LCP 100 turn on another channel of the accelerometer or other sensor(s) in order to analyze a second signal. In different embodiments, LCP 100 may use any of the above described signal(s) in any cascading combination in order to determine whether a tamponade condition is occurring.

Additionally, although the techniques of the present disclosure were described in relation to a maximum amplitude of the signal from the accelerometer or other sensor, in other embodiments, LCP 100 may use different characteristics of the signals. As one example, the value of the integral, or double integral, of the analyzed signal within the sensed window may be used instead of the maximum amplitude of the signal. In these embodiments, the value of the integral or double integral may be compared to one or more thresholds, in a similar manner to that described with respect to the maximum amplitude of the signal, to determine whether a tamponade condition is occurring. In another example, a peak width of a signal may be used. For example, as detailed, above, how long a dP/dt signal stays within a certain percentage of the peak dP/dt signal value may be used to determine if a tamponade condition is occurring.

After determining that a tamponade condition is occurring, LCP 100 may generate an alarm signal or message and communicate the alarm signal to a device external to LCP 100. For instance, where LCP 100 is part of a medical device system, such as system 400, LCP 100 may communicate the alarm signal to external support device 420. External support device 420 may then generate a visual or audible alarm to notify a user in the vicinity of external support device 420 that LCP 100 has determined that a tamponade condition is occurring. In other embodiments, LCP 100 may communicate the alarm signal to another internally implanted device, for instance pulse generator 406, and the other internally implanted device may communicate the alarm signal to a device outside of the patient. In some embodiments, LCP 100, or another device which receives the alarm signal from LCP 100, may be connected to one or more wireless networks. LCP 100, or another device of the system, may connect to the wireless network to communicate the alarm signal to a remote device, such as a pager, cell phone, or other remote device connected to the wireless network.

Additionally, although the above described techniques are centered around LCP 100 performing the sensing and determining functions, where LCP 100 is part of a device system, such as system 400 of FIG. 4, other devices of the system may perform at least some of these functions. For example, LCP 100 may monitor or sense signals from an accelerometer or pressure sensor of the LCP 100 and communicate those signals, or portions of those signals, to another device, such as pulse generator 406. Pulse generator 406 may then determine whether a tamponade condition is occurring. If pulse generator 406 determines that a tamponade condition is occurring, pulse generator 406 may then communicate an indication that a tamponade condition is occurring, for instance as described with respect to LCP 100. In other embodiments, the device doing the determining, based on signals received from LCP 100, may be external support device 406.

Those skilled in the art will recognize that the present disclosure may be manifested in a variety of forms other than the specific embodiments described and contemplated herein. For instance, as described herein, various embodiments include one or more modules described as performing various functions. However, other embodiments may include additional modules that split the described functions up over more modules than that described herein. Additionally, other embodiments may consolidate the described functions into fewer modules.

Although various features may have been described with respect to less than all embodiments, this disclosure contemplates that those features may be included on any embodiment. Further, although the embodiments described herein may have omitted some combinations of the various described features, this disclosure contemplates embodiments that include any combination of each described feature. Accordingly, departure in form and detail may be made without departing from the scope and spirit of the present disclosure as described in the appended claims. 

What is claimed is:
 1. A method for detecting a tamponade condition of a patient's heart after attachment of a leadless cardiac pacemaker to the patient's heart, the leadless cardiac pacemaker having an accelerometer that produces an accelerometer signal, the method comprising: monitoring the accelerometer signal of the leadless cardiac pacemaker; determining if a tamponade condition of the patient's heart is indicated based at least in part on the monitored accelerometer signal, including: identifying a characteristic of the accelerometer signal; determining if the identified characteristic diminishes over time; and determining that the tamponade condition is indicated if the identified characteristics of the accelerometer signal diminishes over time; and in response to determining that the tamponade condition is indicated, providing a notification of the tamponade condition for use by a physician to take corrective action.
 2. The method of claim 1, wherein the identified characteristic comprises a peak amplitude of the accelerometer signal.
 3. The method of claim 1 wherein the identified characteristic comprises a peak amplitude of an integral of the accelerometer signal.
 4. The method of claim 1, wherein the accelerometer signal represents one axis of a multi-axis accelerometer.
 5. The method of claim 1, wherein the accelerometer signal represents a summed signal of all axes of a multi-axis accelerometer.
 6. The method of claim 1, wherein determining if the identified characteristic diminishes over time comprises determining if the identified characteristic falls below a predetermined threshold.
 7. The method of claim 1, wherein the leadless cardiac pacemaker performs the monitoring, determining and providing steps.
 8. The method of claim 1, wherein the leadless cardiac pacemaker performs the monitoring step.
 9. The method of claim 1, wherein an external device programmer performs one or more of the monitoring, determining and providing steps.
 10. The method of claim 1, wherein providing the notification comprises communicating a message from the leadless cardiac pacemaker for reception by an external device programmer.
 11. A leadless cardiac pacemaker for use in pacing a patient's heart, comprising: a plurality of electrodes; an accelerometer for providing an accelerometer signal; a controller operatively coupled to the plurality of electrodes and the accelerometer, the controller configured to: monitor the accelerometer signal of the accelerometer over time; determine if a tamponade condition of the patient's heart is indicated based at least in part on the monitored accelerometer signal, including: identifying a characteristic of the accelerometer signal; determining if the identified characteristic diminishes over time; and determining that the tamponade condition is indicated if the identified characteristic of the accelerometer signal diminishes over time; and in response to determining that the tamponade condition is indicated, communicate a notification of the tamponade condition for use by a physician to take corrective action.
 12. The leadless cardiac pacemaker of claim 11, wherein the notification of the tamponade condition is communicated using two or more of the plurality of electrodes of the leadless cardiac pacemaker.
 13. The leadless cardiac pacemaker of claim 11, wherein the identified characteristic comprises a peak amplitude of the accelerometer signal.
 14. The leadless cardiac pacemaker of claim 11, wherein the identified characteristic comprises a peak amplitude of an integral of the accelerometer signal.
 15. A leadless cardiac pacemaker, comprising: a plurality of electrodes; an accelerometer for providing an accelerometer signal; a controller operatively coupled to the plurality of electrodes and the accelerometer, the controller configured to: monitor an indication of a range of physical motion of a patient's heart over time using the accelerometer signal; determine if the indication of the range of physical motion of the patient's heart reduces over time by at least a predefined amount; and if it is determined that the indication of the range of physical motion of the patient's heart has reduced over time by at least the predefined amount, communicate a notification of a possible tamponade condition for reception by a remote device that is remote from the leadless cardiac pacemaker.
 16. The leadless cardiac pacemaker of claim 15, wherein the controller is further configured to monitor a heart rate of the patient's heart over time and to determine if the heart rate increases over time by at least a predetermined heart rate amount.
 17. The leadless cardiac pacemaker of claim 16, wherein the controller only communicates a notification of the possible tamponade condition if it is determined that the indication of the range of physical motion of the patient's heart has reduced over time by at least the predefined amount and the heart rate of the patient's heart has increased over time by at least the predetermined heart rate amount.
 18. The leadless cardiac pacemaker of claim 15, wherein the notification of the possible tamponade condition is communicated using two or more of the plurality of electrodes of the leadless cardiac pacemaker. 